Recently, electronic parts such as an IC's and the like used in an electronic instruments have become more integrated and operate at higher clock speeds, which increases the electricity consumption and heat generation. This is one cause of misoperation of the electronic instrument and failure of the electronic parts themselves and heat dissipation of those electronic parts is now a major concern.
Heretofore, a heat sink made of a metal plate with high heat conductivity, such as brass and the like, has been used in an electronic instrument, in order to suppress temperature rise of the electric instrument during use.
The heat sink conducts the heat generated from the electronic parts and dissipates the heat from its surface by the temperature difference between the surface and the outside atmosphere. In order to efficiently conduct the heat from the electronic parts to the heat sink, it is necessary for the heat sink to closely contact the electronic parts. Because of differences in height among the electronic parts and tolerances in the assembly, soft heat-conductive sheets are disposed between respective electronic parts and the heat sink to attain good heat conduction from the electronic parts to the heat sink via the heat-conductive sheets. For example, one side of a heat conductive sheet made of heat-conductive silicone rubber and the like is made to adhere closely to each electronic part, and the other side is made to closely contact with a metal plate, for example a box panel, a common heat sink.
The aforementioned heat conductive sheet, which is to be applied to an electronic part on a printed circuit board in an assembly line, cannot be automatically mounted but is applied to the printed circuit board by hand.
The reason why the heat conducive sheet cannot be automatically mounted is that the heat conductive sheet has adhesive for adhering to the parts. An attempt at automatic mounting may cause the heat conductive sheet to adhere to the automatic mounting reel and the like. Usually, the adhesive surface of a heat conductive sheet is covered with a protective sheet. When mounting is performed by hand, the protective sheet is first peeled off and then the heat conductive sheet is applied. The peeling of the protective sheet will also hindered automatic mounting. When mounting is performed by hand, heat conductive sheets with various shapes, sizes and thicknesses need to be applied to the electronic parts. As the size of electronic parts is becoming smaller, the mounting work is becoming more troublesome and labor consuming.